Method of formation consolidation



United States Patent ,l2l.,462v METHUZD 0F FORMATHQN CGNSOLIDATIONWilliam L. Martin, .lohn D. Alexander, and John N. Dew,

Ponca City, his assignors to Continental Gil Company, Ponca City, Gilda,a corporation of Delaware llo Drawing. Filed .Qept. 17, 1959, Ser. No.840,519 6 Claims. (Cl. 166-29) This invention relates to the treatmentof wells such as those producing oil or gas wherein the fluid producingformation is an unconsolidated or poorly consolidated sand or sandstone.More particularly it is directed to an improved method of consolidatingsuch formations by a method which will not cause a prohibitive reductionin the permeability of the formation.

In the production of fluids from subterranean geological formations,difficulties are often encountered because cer tain of the producingformations are composed of unconsolidated sands or loosely consolidatedsandstone. The presence of such unconsolidated sands in the productionzone surrounding the well bore causes several types of problems in thecompletion and production of such wells. The production of fluids from awell which is based in such a formation frequently results in theconcurrent production of sand particles which is undesirable because theunconsolidated formation fills the well bore with said particles, thusblocking the Well bore and restricting the production therefrom. Thedamage is also extended to the pumps and surface lines of the productionfacilities above the well hole because of the abrasive and erosiveactions of the sand grains and particles entrained in the fluids whichare produced. The normal methods of production do not providesatisfactory results when applied to these sand formations and it hasbecome necessary to develop new production methods specifically designedfor such formations.

Previous efforts have heretofore been attempted for consolidating such aformation surrounding a well bore. Although certain of the methodsproposed heretofore accomplish the desired sealing or cementing of theuncou solidated sands, the result is a formation that has only a slightpermeability to oil or gas. The known methods of reducing sandproduction have all achieved a certain degree of success, but there arelimitations which none of the methods have been able to overcomesuccessfully. Furthermore, the degree of such success is more reducedwhen the conditions of temperature and corrosion are greater thannormal.

It is therefore a primary object of the present invention to provide amethod of consolidating incompetent oil and gas formations which obviatethe disadvantages of the prior art methods, especially under conditionsof high temperatures, corrosion, and erosion.

Another object of our invention is to provide an im* proved method forconsolidating loose sand formations with the maximum retention andutilization of the porosity and permeability characteristics of the sandwithin the formation surrounding the well bore.

Another object of this invention is to provide a method of wellcompletion for primary or secondary recovery Wells which will allow themto be subjected to repeated clean-out by in-well or near-well combustionwithout disrupting the formation production facilitie ther objects andadvantages of this invention will become apparent during the course ofthe following de* scription.

This invention broadly relates to an improved method of consolidationcapable of achieving the above objects by treating incompetenthydrocarbon producing forma tions to effect the placement or creation ofa permeable,

eramic-type consolidated zone surrounding the well bore penetrating saidunconsolidated formation.

EidZlAdZ Patented Feb. 18, 1964 One embodiment of this invention is tosubject said formation surrounding the well bore to in situ combustionfollowed by the injection of a heat refractory cement into a zoneimmediately surrounding the well bore and pro duction of the formation.Another embodiment of the invention comprises in situ combustion, asabove, followed by the injection of a silicate binder and production ofthe formation. The invention may be embodied also in a solvent treatmentof the formation surrounding the Well bore followed by the injection ofa heat refractive cement and production of the formation. Still furtherembodiment of the invention comprises subjecting the formation tosolvent wash, as above, followed by the injection of a silicate binderand production of the formation.

All sand consolidation agents are more effective when applied toformations which have been made devoid of all water and residual crudeoils, but this ideal condition has not been previously obtainable infield operations. The improved method disclosed herein allows theincompetent formation to be placed in the above ideal condition and moreeffectively treated by one of the alternate approaches. Therefore thefirst step of this improved method of well treatment is to clean thesand grains and particles of the incompetent formation to the desireddistance about the well bore. This can be accomplished by conducting insitu combustion, or by subjecting said zone about the well bore to asolvent wash.

The approach to rendering the incompetent zone about the Well boredevoid of all but clean unconsolidated sand grains and particles can beaccomplished effectively by in situ combustion as known in the art. Insitu combustion requires that the formation have suificient combustiblematerial, combustion supporting gas, and an ignition level temperatureprior to initiation. This can be accomplished by any known means; suchas injecting or utilizing situ hydrocarbons; injecting air; and heatingthe air to the required temperature with heating means, such as downholeheater. After ignition of the combustion, the in jection of acombustion, the injection of a combustion supporting gas is continued tomove the resultant combustion front outwardly from the Well bore to thedesired distance from one (1) to twenty (20) feet, preferably in theorder of five (5) feet. The leading edge of the combustion front ischaracterized by a temperature gradient of 700 to 1500 F./ft., whichdistills and cracks all liquids within the formation causing them to bedriven ahead of the front. The cracking results in the deposition of asmall portion of the residual hydrocarbons in the formation in the formof petroleum coke which is also combusted and removed as fuel for thefront as it passes said coke.

The sand grains and particles and the pore spaces of the zone which havebeen subjected to the in situ combustion are thoroughly cleaned and theresult is the desirable clean unconsolidated sand which is prepared forconsolidation because the passage of said front through a zone removesall liquids and combustible material therefrom. The formation radiallyahead of the point where the combustion is terminated is characterizedby a zone of coke followed by an oil saturated zone which suppliescertain cohesive properties to that portion of the formation.

The invention herein discloses the other approach to cleaning the sandto be that of conventional solvent washout by injection and flushing toremove all material from the sand grains and particles. Solventssuitable for the dissolution and removal of hydrocarbons, such as carbondisulfide, acetone, benzene, etc., are injected under pressure to movethe hydrocarbonaceous material away from the well bore either to thesurface or into the formation.

The injection is continued until a sufiicient amount of solvent isinjected, whereupon air or gas is injected to cause the solvent to beevaporated or driven further into the formation.

A portion of the incompetent formation, upon being made devoid of allhydrocarbons and other liquids by either of the above approaches, isthen in condition to be subjected to efforts of consolidation. Thisconsolidation can also be conducted in one of several manners disclosedhereinbelow as a step in the method of this invention, in order that thedesired porous, permeable synthetic sandstone, either the sand and therefractive cement, or the loose sand and the consolidating binder, canbe established within the formation. Upon completion of the step ofrendering the incompetent formation devoid of undesirable matter as setforth above, the next step is to consolidate the sand grains andparticles so that orderly production may be established and maintainedin the formation. The portion of the formation about the well bore whichhas been rendered even more incompetent by the cleaning effect ofsolvent injection or combustion consists solely of loose sand grains andparticles which must be further treated.

The clean, unconsolidated sand of said formation is transformed into aconsolidated formation capable of efficient production by one of twoalternate approaches disclosed herein. The first approach toconsolidation requires a portion of the unconsolidated sand about thewell bore to be removed to the desired distance, which can beaccomplished by conventional means such as bailing or reversecirculating with fluids. This removal of sand is accomplished within theformation outwardly from the well bore to establish a cavity about saidwell bore. The cavity may be extended to a diameter equal to distance towhich in situ combustion or solvent injection has been conducted, but ineither case the outer periphery of the cavity is supported by either thecoke created by the combustion or the cohesive mixture of unconsolidatedformation and formation hydrocarbons. After the removal of said cleansand grains and particles from about the well bore, the void of thecavity is substantially filled, by dumping or pumping, with a mixture ofhighly refractive silica cement and sand. The cement can be injected bynormal pumping means and the sand mixed therewith is properly controlledin order that the desired features of porosity and permeability areobtained. This creates a cement plug of a permeable, ceramic type in andabout the well bore which effectively consolidates the formation and iscapable of withstanding severe conditions of corrosion aggravated byelevated temperatures. The porosity and permeability of the cement plugmay be further increased by injecting air through the plug during theperiod of dehydration and setting. This plug is thereafter drilledthrough subsequent to suificient setting and production is accomplishedthrough the remainder of the ceramic type of consolidation of thissynthetic sandstone within the surrounding incompetent formation.

The consolidation of a formation using a highly refractive cement mayalso be utilized without the initial step of cleaning the formation withsolvents or combustion, providing the formation characteristics are suchthat a sufficient cavity can be created by conventional means withoutthe initial removal of the naturally occurring co hesive factors.

A second approach to consolidating the previously cleaned incompetentformation is to inject therein a suitable silicate binder, such as anaqueous solution of sodium silicate. The binder is injected through thewell bore under pressure by conventional means in sufficient amounts toextend throughout the formation surrounding said well bore to thedesired distance. Immediately subsequent to the injection of saidbinder, air or another nonreactive gas is injected to control andachieve the proper saturation of the clean sand with binder to createpermeability throughout the zone, and to effect a partial drying of thebinder within the pore spaces. Thereafter, an acid, preferably a strongmineral acid such as hydrochloric, in the aqueous or anhydrous gaseousstate is injected into the formation where it reacts with the previouslyinjected binder. The reaction of the acid and binder causes the sandgrains and particles to be consolidated by the creation of insolubleacid silicates which are precipitated in such a manner as to establish apermeable, ceramic-type zone of consolidated formation surrounding thewell bore. The conversion reaction to insoluble silicate may be carriedto completion by injecting dry air which has been heated to about 300 F.

Subsequent to the establishment of the desired consolidated zone ofsynthetic sandstone by the above efforts, the formation is returned toproduction in the normal manner as known in the art. This productionwill be free from the concurrent production of sand grains and particlesand there will accordingly be increased production rates and economics.The previously incompetent formation is thereby rendered competent andthe permeability and porosity of the predominant sand grains andparticles are retained to allow production to be accomplished in anefiicient and effective manner without the previous concurrentundesirable grain and particle production.

Furthermore the method disclosed herein can be utilized indefinitelybecause the consolidated portion of the formation which has been createdin sufficiently heat and corrosion resistant that it may bere-conditioned, as necessary, by initiating in situ combustion in ornear said well bore to remove any undesirable deposits which accumulatein the synthetic sandstone. Therefore the formation may be maintained asproducing one for an indefinite period in this state of improvedefficiency with a maximum of maintenance economy.

In order to disclose the nature of the present invention still moreclearly the following illustrative examples will be given. It is to beunderstood that the invention is not to be limited to the specificconditions or details set forth in these examples except insofar as suchlimitations are specified in the appended claims.

Example 1 The well has been drilled to a depth at which the well boreexists in a producing stratum of a formation which is composed ofunconsolidated and loosely packed sand. A screen or slotted liner isthen installed in the well bore in preparation for cleaning theunconsolidated sand of the surrounding formation by the method of insitu combustion. The well, bore is fitted with a burner or bottom holeheater of the proper capacity, and in situ combustion conducted by meansknown in the art. The combustion process may be supplemented bycontinuing to inject hot gases containing oxygen to accomplish thecleaning to a distance of five feet. The Well is kept clean and dry andis cooled by the continued injection and circulation of air in the wellbore. An amount of aqueous solution of sodium silicate sufficient topartially saturate the cleaned sand is then injected with air pressureas required until the sodium silicate is distributed throughout thecleaned sand. Air saturation and permeability is created by additionalair injection for a sufficient time to permit a partial drying of thesilicate solution in the formation, at which time a dilute liquid orgaseous mixture of hydrochloric acid, is injected in sufficient quantityto form silicic acid which converts ultimately to silicon dioxide. Thesereactions may be illustrated by Equations 1 and 2:

(2) Heat zmsioi 2Si02 47120 These reactions show the types of reactionswhich take place and various forms of the silicates react in thesegeneral Ways. Hot or cold air is injected until suihcient time isafforded for completion of these reactions and the acid silicate isirreversibly dehydrated, as represented by Equation 2, whereupon thewell is returned to production.

Example 2 The consolidation method described in Example 1 isaccomplished in exactly the same manner except with reference to themethod used to clean the unconsolidated sand of the formation. Thecleaning is done by washing the well out with any of the availablesolvents, such as benzene, toluene, carbon disulfide, acetone, orlow-cost solvent cuts available from a petroleum refinery, and thenapplying suflicient air pressure to force the solvent out into theformation. The well is then closed, dried out and completed as inExample 1.

Example 3 The unconsolidated sand of the formation is cleaned asdescribed in Examples 1 or 2, but another technique of well completionis used. A portion of the clean loose sand of the formation is removedfrom about the well here by any conventional method. A mixture of cleansilica sand and a high temperature ceramic cement, such as No. 31Sauereisen cement, is dumped or pumped into the hole under pressure. Thesand and cement mixture form a consolidated zone in the cavity where theclean sand was removed and after it has been allowed to set up, the wellbore is extended through the plug by drilling and the well is completedin a conventional manner.

Example 4 The reservoir contains a sufficiently heavy crude oil, or isotherwise sufficiently competent, so that the unconsolidated loose sandsurrounding the well bore is removed without prior cleaning in an amountsulhcient to create an area in which high temperature refractory cementmay be injected. This removal is accomplished by jetting or underreamingthe mea around the well bore and the cement of the type set forth inExample 3 is utilized with well completion following in the normalmanner, i.e., behind pipe or as a permeable cement plug- 6 back withsubsequent open hole completion through the plug after extending thewell bore by drilling.

It will be understood that the examples included herein are illustrativeonly and that the invention is to be taken as limited only by the scopeof the appended claims.

We claim:

1. A method of consolidating an incompetent formation of unconsolidatedor loosely consolidated sands and clays traversed by a well bore whichcomprises the steps of cleaning a portion of said formation surroundingthe well bore; injecting a silicate binder into the clean sandsurrounding the well bore; injecting a nonreactive gas into saidformation to achieve permeability and dry the binder; and injecting anacid into the formation which forms a consolidated permeable poroussynthetic sandstone within the formation.

2. The method in accordance with claim 1 wherein the silicate binder isan aqueous solution of sodium silicate.

3. The method in accordance with claim 1 wherein the nonreactive gasinjected into the formation and binder 1S arr.

4. The method in accordance with claim 1 wherein the nonreactive gasinjected into the formation and binder is air heated to a temperature of300 F.

5. The method in accordance with claim 1 wherein the acid injected is astrong mineral acid.

6. The method in accordance with claim 1 wherein the acid injected is ahydrochloric acid.

References Cited in the file of this patent UNITED STATES PATENTS2,019,908 Kennedy Nov. 5, 1935 2,207,759 Reimers July 16, 1940 2,241,254Garrison May 5, 1941 2,378,817 Wrightsrnan et al June 19, 1945

1. A METHOD OF CONSOLIDATING AN INCOMPETENT FORMATION OF UNCONSOLIDATEDOR LOOSELY CONSOLIDATED SANDS AND CLAYS TRAVERSED BY A WELL BORE WHICHCOMPRISES THE STEPS OF CLEANING A PORTION OF SAID FORMATION SURROUNDINGTHE WELL BORE; INJECTING A SILICATE BINDER INTO THE CLEAN SANDSURROUNDING THE WELL BORE; INJECTING A NONREACTIVE GAS INTO SAIDFORMATION TO ACHIEVE PERMEABILITY AND DRY THE BINDER; AND INJECTING ANACID INTO THE FORMATION WHICH FORMS A CONSOLIDATED PERMEABLE POROUSSYNTHETIC SANDSTONE WITHIN THE FORMATION.